In order to produce an aqueous coating composition having satisfactory adhesiveness and compatibility with a fluorine-based resin, it has been proposed to use an emulsion formed from a copolymer obtained from tertiary butyl (meth)acrylate an ethylenically unsaturated carboxylic acid monomer and other ethylenic monomer (see, for example, claim 1 and paragraph [0001] of Patent Document 1).
It is reported that when the above-mentioned emulsion is mixed with a fluororesin-based emulsion, the above-mentioned emulsion and the fluororesin-based emulsion have satisfactory compatibility with each other, and a mixture obtained by mixing both emulsions has satisfactory adhesiveness to a mortar board and a slate board (see, for example, paragraphs [0035] to [0046] of Patent. Document 1).
However, the above-mentioned emulsion has a defect such that the emulsion is poor in film-forming property at low temperatures, extensibility and warm water freezing stability (see, for example, comparative example 1 of the present specification).
Accordingly, in recent years, it has been desired to develop a film-forming auxiliary which is comprehensively excellent in film-forming property at low temperatures (low-temperature film-forming property), warm water resistance, extensibility, weather resistance, coating property on a vertical surface (vertical-surface coating property) and warm water freezing stability.